The present invention generally relates to water recovery and purification apparatus and methods for providing potable water from a gas.
Ambient air may provide a convenient source of potable water in certain environments. Exhaust gas from an internal combustion engine may comprise about 10% by volume of water, and may provide a relatively large supply of water. Engine exhaust from vehicles may provide a mobile supply of water from an existing source. The recovery of potable water from air or engine exhaust is of advantage in remote areas, which lack reliable supplies of clean water, and to the military.
While engine exhaust contains higher concentrations of water as compared with ambient air, exhaust gas also contains various pollutants which must be removed to provide relatively pure, potable water. However, current systems for water recovery are inefficient; that is, the energy cost or weight and size of the system is high, while the quality of the recovered water is relatively poor. One problem encountered in recovering water from engine exhaust is that the exhaust gas typically contains many types of impurities that are not removed by a single device. For example, engine exhaust may include organic particulates (soot); organic vapors, such as fuel and partially combusted fuel; metals from the engine; and inorganic compounds, such as nitrogen oxides formed from nitrogen in air, and sulfur oxides formed from sulfur in fuel. Engine exhaust may further include compounds ingested into the engine from the environment, including compounds found on a battlefield such as smoke and chemical warfare agents.
Prior art devices for water recovery and purification from gases require frequent maintenance or have low efficiency when used for recovering potable water from engine exhaust streams. For example, membranes and filters for removing particulates clog frequently due to the accumulation of soot, and furthermore generally do not remove low molecular weight organic compounds. Adsorptive filters for removing organic compounds have finite capacity and need to be replaced as consumable items.
U.S. Pat. No. 2,479,766 to Mulvany discloses a water recovery system for recovering water from engine exhaust during aircraft flight, in which water is separated by a water separator, and cooling for condensation is provided by slipstream air. U.S. Pat. No. 4,725,359 to Ray discloses a water recovery apparatus for recovering water from engine exhaust in which a membrane is used to separate water, in the form of a water vapor permeate stream, from the exhaust gas.
U.S. Pat. No. 4,656,831 to Budininkas et al. discloses a water recovery apparatus for recovering water from engine exhaust in which water is separated from the exhaust via a condenser, and the water is passed through an ion exchanger on a limestone bed. U.S. Pat. No. 6,581,375 to Jagtoyen et al. discloses a water recovery apparatus for recovering water from the exhaust of a vehicle in which the vehicle's catalytic converter is used to remove pollutants from the vehicle exhaust, and water condensed from the exhaust is filtered through particulate filters, passed through activated carbon beds, and passed through ion exchange resin beds. Both Budininkas et al. and Jagtoyen et al. require the exhaust temperature to be preferably at least about 700° F. for operation of the apparatus, due to the temperature requirements of the catalytic converter.
As can be seen, there is a need for a water recovery system and method for water recovery and purification from a gas stream that is broadly applicable to both non-vehicle applications and vehicle applications, including aircraft and land vehicles, whether stationary or moving, and to gas turbine engines, diesel engines, and gasoline engines. There is a further need for a water recovery system and method that is energy efficient, is not restricted by operational conditions, uses minimal amounts of consumable materials and components, and requires minimal maintenance. There is a further need for a water recovery system that can be operated regardless of engine- or exhaust gas temperature, and which is applicable to ambient air as well as exhaust gas.